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MSc WLAN, IP/TCP and COMM NETWORK Topics

By Prof R A Carrasco School of Electrical ,Electronic and Computer Engineering University of Newcastle Upon Tyne. MSc WLAN, IP/TCP and COMM NETWORK Topics. r.carrasco@ncl.ac.uk Ext: 7332. MSc WLAN, IP/TCP and COMM NETWORK. References

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MSc WLAN, IP/TCP and COMM NETWORK Topics

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  1. By Prof R A Carrasco School of Electrical ,Electronic and Computer Engineering University of Newcastle Upon Tyne MSc WLAN, IP/TCP and COMM NETWORKTopics r.carrasco@ncl.ac.uk Ext: 7332

  2. MSc WLAN, IP/TCP and COMM NETWORK References [1] Tanenbaum, Andrew S., Computer Networks, Fourth Edition ed: Pearson Education International, 2003,ISBN: 0-13-038488-7. [2] Comer, Douglas E, Computer Networks and Internets with Internet Applications, Third Edition ed: Prentice Hall, 2001, ISBN: 0-13-091449-5. [3] Peterson, Larry L. & Davie, Bruce S., Computer Networks, A Systems Approach: Morgan Kaufman Publishers, 2000, ISBN: 1-55860-577-0. [4] Halsall, Fred, Data Communications, Computer Networks and Open Systems: Adison-Wesley Publishing, 1995, ISBN: 0-201-42293-X

  3. Internet and Protocols • Advanced Research Projects Agency Network (ARPAnet), 1969. • The protocols in the TCP/IP suite either use transport control protocols (TCP) or • user datagram protocol (UDP) as the transport protocol. • Low level functions such as File Transfer Protocol (FTP), the Internet Terminal • Protocol (TELNET) and Electronic Mail (E-Mail), remote logon. • IP is responsible for moving packets of data from node to node. IP forwards each • packet based on a four byte destination address (the IP number), different • organisation, IP operates on a gateway machine. • TCP is responsible for verifying the correct delivery of data from client to server. • TCP adds support to detect errors or lost data to trigger retransmission until the • data is correctly and completely received. • Sockets is a name given to the package of subroutines that provide access to • TCP/IP on most systems

  4. The Internet Protocol was developed to create a Network of Networks (the • Internet). Individual machines are first connected to a LAN (Ethernet or Token • Ring). TCP/IP shares the LAN with other users. One device provides the TCP/IP • connection between the LAN and the rest of the World. • A Network consisting of two or more far-apart LANs is a Wide Area Network (WAN) • Typical Network consisting of Switches, Hubs and Routers are intermediary • devices between clients and servers

  5. The Network Layer in the Internet • The Internet can be viewed as a collection of sub-networks or autonomous systems (AS) that are connected together • There is not real structure, but several major backbones exist • These are constructed from high-bandwidth lines and fast routers • Attached to the backbones are regional networks, and attached to these regional networks are LANs (Universities, companies etc.) • The glue that holds the Internet together is the network layer protocol, IP

  6. The Network Layer in the Internet • The Internet transmits data by packet switching using a standardised Internet Protocol (IP) • IP Datagram The header has a 20-byte fixed part and a variable length optional part • It is transmitted in big edian order from left to right with higher-order bit of the version field going first

  7. Ethernet hub is a device for connecting multiple twisted pair or fibre Ethernet devices together.

  8. [2] D. E. Comer, "Computer Networks and Internets with Internet Applications," Prentice Hall, 2001, pp. 157-167. Ethernet bridge connects multiple network segments at the data link layer ( layer 2 ) of the OSI model. http://netbook.cs.purdue.edu/anmtions/anim09_2.htm

  9. A router is a computer networking device that forwards data across networks towards their destination, through a process known as routing. http://netbook.cs.purdue.edu/anmtions/anim09_3.htm

  10. Modem is a device that modulates an analogue carrier signal to encode digital information and also demodulate such a carrier signal to decode the transmitted information.

  11. A. S. TanenBaum, "Computer Networks," Pearson Education, 2003, pp. 234-243, pp. 16-26, pp. 271-291. [1] Popular Wired LAN Standards • High-Level Data Link Control (HDLC) • Ethernet (IEEE 802.3) • Token Bus (IEEE 802.4) • Token Ring (IEEE 802.5)

  12. 8 8 8 >0 16 8 01111110 Checksum 01111110 Data control address A. S. TanenBaum, "Computer Networks," Pearson Education, 2003, pp. 234-243. [1] Frame format for bit-oriented protocols. HIGH LEVEL DATA LINK CONTROL

  13. 3 3 3 1 1 1 3 3 3 1 1 1 Type Seq Type Next Modifier Next P/F P/F P/F 0 0 0 (a) (c) (b) A. S. TanenBaum, "Computer Networks," Pearson Education, 2003, pp. 234-243. [1] HIGH LEVEL DATA LINK CONTROL(2) • Control Field of • An information frame • A supervisory frame • An unnumbered frame

  14. 1 1 1 1 or 2 2 or 4 1 Variable Flag 01111110 Address 11111111 Flag 01111110 Control 00000011 Payload checksum Protocol The PPP full frame format for unnumbered mode operation PPP- Point to Point Protocol Bytes

  15. Ethernet (IEEE 802.3) • Bus Topology • Carrier Sense Multiple Access with Collision Detection (CSMA/CD) • 10 Bases denoting 10 Mbit/s http://netbook.cs.purdue.edu/anmtions/anim06_1.htm

  16. Tap Transceiver Drop cable MAC Unit Protocol Firmware Network Service Ethernet (IEEE 802.3)

  17. TYPE PR SFD DA SA INFORMATION FCS Data frame Ethernet (IEEE 802.3) • PR = Preamble • SFD = Start Frame Data • DA = Destination Address • SA = Source Address • TYPE = Type of data • FCS = Frame Checksum

  18. CSMA/CD MAC Protocol • Station checks if there is data being currently transmitted (carrier sense) • If no data is present, station begins to transmit data • If two or more stations begin this process simultaneously, there will be a collision of frames • Station monitors its own receiver output and compares with transmitted signal to detect when this occurs (collision detection) http://netbook.cs.purdue.edu/anmtions/anim06_2.htm http://netbook.cs.purdue.edu/anmtions/anim06_5.htm

  19. CSMA/CD MAC Protocol • If a collision is detected, the station aborts the transmission and sends a jamming signal to inform all other stations that a collision has occurred • Transmitting stations that have caused the collision wait a randomly generated time interval before reattempting to transmit • This avoids step-lock in terms of retransmission causing repeated collisions

  20. Capacity Calculations  TX - A TX - B Time T = Transmitted frame length A B  delay

  21. Capacity Calculations Time to transfer information Collision interval  2 TX-A TX-B Sensing time Time to detect collision The maximum propagation delay to frame length ratio a =  / T The figure above allows a new frame to be transmitted immediately following the previous one, giving a frame rate of 1/T frames/sec

  22. Capacity Calculations • If, on average K retries are necessary before the next frame can be transmitted (in a lightly loaded network k=0), then the average time for transmitting one frame, tv, is given by: • tv = T +  + 2K = T + (1 + 2K) = T [1 + /T(1 +2K)] = T[1 + a(1+2K)] Where a=/T

  23. Capacity Calculations • The utilisation factor, U, of the transmission medium is given by: • U = T/tv = 1/(1+a(1+2k)) • Let Pt be the probability constant for all stations over all time that any particular station wishes to transmit at the end of a specific 2 collision detection interval • Pt = 2 λ ,(where λ is the rate of packets/s)

  24. Capacity Calculations • For a successful event, one station transmits, but n-1 stations do not • The probability of n successful transmissions p is therefore given by: p = nPt(1 - Pt)n-1 • It can be shown by differentiating p with respect to Pt that the maximum value of the probability Pt is: Pt = 1/n Where n is the number of stations

  25. Capacity Calculations • Consequently the maximum value of p is given by: • pmax= n  1/n(1 – 1/n)n-1 = (1 – 1/n) n-1 • If n→∞ then pmax→ 1/e where e = 2.718… • At the end of a 2 collision detection interval, a further collision occurs with probability 1-p, while a successful transmission occurs with probability P • Thus, a sequence of K collision intervals occupying a time 2K sec, occurs with probability: • P (k) = p(1-p)K-1 at least one collision occurring

  26. Capacity Calculations • The average number of collisions is therefore given by: • k= Σk=1kp(k) = Σk=1kp(1-p) k-1 • From this it can be proven that k=1/p, and we obtain the limiting utilisation: • U = T/tv = 1/(1+a(1+2k)) • Umax = 1 / (1+a(1+22.718)) = 1/(1+6.44a)

  27. Utilisation with different values for the a parameter a a

  28. Ethernet Exercises • Problem: A certain Ethernet system has a maximum bus delay of 16 μsec, and operates with a bit rate of 10 Mbit/sec. Each frame is 576 bits in length. Determine the maximum utilisation factor of the medium under collision conditions • For the system above, calculate the actual capacity if there are 15 active stations, each with an equal amount of data to transmit

  29. Token Ring (IEEE 802.5) Ring Structure SD AC FC DA SA INFORMATION FCS ED FS Data frame SD AC ED Token frame http://netbook.cs.purdue.edu/anmtions/anim06_4.htm

  30. Token Ring Frame Structures • SD = Start Delimited (1 octet) • AC = Access Control (1 octet) • FC = Frame Control (1 octet) • DA = Destination Address (2/6) • FCS = Frame Check (4) • ED = End Delimiter (1) • FS = Frame Status (1)

  31. Trunk Coupling Unit (TCU) Ring cable Drop cable MAC Unit Protocol Firmware Network Service Token Ring

  32. D D Free Token C A C A B B D D A C A C B B Token Ring A removes the data frame A generates data frame for station A Busy Token Free Token

  33. Capacity Calculations • Empty Ring • C = Capacity (bits/sec) •  = Propagation time around ring • N = Number of stations • L = Delay of L bits in each station on the ring (station latency)

  34. Capacity Calculations • The ring latency is given by: • TL =  + (NL)/C • The free token is 24 bits (3 bytes) in length, thus the maximum waiting time, if no other station is transmitting, is given by: • Tmax,empty = (24/C + TL)

  35. Capacity Calculations • Full Ring • Consider a full ring, where all stations have data to transmit • Each station can only transmit when it has the token • If each frame is limited to M bytes, the transmission time is: • T = 8M/C • The maximum waiting time is: • Tmax, Full = (N-1)(T+TL)

  36. Capacity Calculations • Exercise • A 4Mbit/s ring has 50 stations, each with a latency of 2 bits, the total length of the ring is 2km, and the propagation delay of the cable is 5μs/km • Determine the maximum waiting time when the ring is empty, and when all stations are transmitting. A full frame is 64 bytes in length

  37. Capacity Calculations • Loaded Ring • Traffic load of λi frame/sec • T = Time when transmitted on the ring for each frame • Tc = time interval elapsed before the free token arrives • ti = λiTcT

  38. Capacity Calculations • The maximum waiting time experienced by every station on the ring Tc is given by: • Tc = TL + ΣNi=1ti = TL + tcΛT • Where Λ = ΣNi=1 λi • Here the parameter Λ represents the gross input to the ring in frame/sec • Tc/TL = 1 / (1-U) and U = ΛT

  39. Tutorial: Network Systems and Technologiesby Professor R. A. Carrasco • 1)      Describe the basic differences between a wide area network and a local area network in terms of: • a)      Structure • b)      Operation • 2)      The techniques of passing information from node to node across a broadcast network differ according to the type of configuration employed. Compare the methods used for bus and ring networks. • 3)      a) What is a baseband LAN? •     What is a broadband LAN? b) What are the advantages of using a star ring architecture in a computer network? What are its disadvantages? • 4)      Describe the effects of a complete failure of a node in the operation of the following network configurations: • a bus • a ring • a star • 5)      List the seven layers of the CCITT ISO architecture for network communications. • a)      Describe their function and justify the existence of each one. • b)      Which layers are essential to LAN communications and why?

  40. 6)      Assuming HDLC protocol • a)      Distinguish between the normal response mode and the asynchronous mode of working. How are they defined in the HDLC frame structure? • b)      How is flow control achieved through this frame structure? • 7)      Describe the function of the logical link control and medium access control layers as defined in the IEEE 802 standards and indicate their relationship with the lower protocol layers in the ISO seven-layer reference model. 8)      a) Describe the basic differences between circuit switching, message switching and packet switching. b) Give examples of each switching technique. Advantages and disadvantages of switching  techniques. c) For packet switching technique: give an example. How will the network handle stream of packets? • 9)      i) Discuss IEEE 802 standards and frame format for CSMA/CD, token bus, token ring, 802.2 (logical link control), 802.3, 802.4 and 802.5 standards. ii) Briefly discuss the comparison of 802.3, 802.4 and 802.5 standards. • 10)  Imagine two LAN bridges, both connecting a pair of 802.4 networks. The first bridge is faced with 1000 512-byte frames per second that must be forwarded. The second is faced with 200 4096-byte frames per second. Which bridge do you think will need the faster CPU? Discuss. • 11)  Suppose that the two bridges of the previous problem each connected an 802.4 LAN to an 802.5 LAN. Would that change have any influence on the previous answer?

  41. 12)  A bridge between an 802.3 LAN and an 802.4 LAN has a problem with intermittent memory errors. Can this problem cause undetected errors with transmitted frames, or will these all be caught by the frame checksums? • 13)  A large FDDI ring has 100 stations and a token rotation time of 40 msec. The token holding time is 10 msec. What is the maximum achievable efficiency of the ring?

  42. [1] A. S.TanenBaum, "Computer Networks," Pearson Education, 2003, pp. 26-49.

  43. The Internet uses almost exclusively TCP for layer 4 and IP for layer 3 • Clients and servers typically implement all of the seven OSI layers whilst • hubs and switches are only aware of MAC addresses • Routers are aware of network address (IP addresses), a layer 3 switch is really • a fast router • Routing protocols differ from routed protocols since they dynamically determine • routing and the route taken by one packet can be different to that of another • packet taking place in the same transaction. • Transmission Control Protocol (TCP) is a transport layer protocol layered on top • of IP and below the application layer SMTP, Telnet, FTP, HTTP(web) etc.

  44. Transmission Control Protocol (TCP) • (RFC 793) • Van Jacobson’s algorithm • Karn’s algorithm • Nagle’s Algorithm

  45. ISO/OSI TCP/IP Application Application Presentation Session Transport Transport Network Network (IP) Data Link Ethernet Physical IEEE 802.2 IEEE 802.5 IEEE 802.6 IEEE 802.3 IEEE 802.4 IEEE 802.x, TCP/IP and ISO/OSIArchitecture Comparison IEEE 802.x

  46. FTP (File Transfer Protocol) SMTP (Simple Mail Transfer Protocol) FTP is used to connect two computers over the internet so that users of one computer can transfer files and perform file commands on the other computer. Simple Mail Transfer Protocol is the de facto standard for e-mail transmission across the internet. This is a text based protocol. SMTP uses TCP port 25. TELNET (TELe type NETwork) TELNET is a network protocol based on the internet or the local area network (LAN) connections. The term telnet also refers to software which implements the client part of the protocol.

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